Tetrabromobisphenol-A is 4,4'-isopropylidenebis(2,6-dibromophenol). It is a widely used commercial fire retardant. There have been numerous publications on how it can be made. Hennis, U.S. Pat. No. 3,234,289, describes a process in which bisphenol-A (i.e. 4,4'-isopropylidenebisphenol) is placed in a water-alcohol mixture and liquid bromine is added at 22.degree.-28.degree. C. followed by reflux. Majewski et al., U.S. Pat. No. 3,363,007, discloses a process for brominating bisphenol-A in a mixture of water and an alkyl ether of a lower glycol.
Asadorian et al., U.S. Pat. No. 3,546,302, discloses a bromination process conducted in a two-phase solvent having an aqueous phase and an organic phase.
Montanari et al., U.S. Pat. No. 3,868,423, discloses the bromination of isopropylidenebisphenol with liquid bromine and gaseous chlorine in a methanol solvent. Janzon et al., U.S. Pat. No. 3,929,907, discloses the bromination of bisphehols in the presence of aqueous hydrogen peroxide.
Brackenridge, U.S. Pat. No. 4,013,728, teaches a process for brominating bisphenol-A in aqueous acetic acid followed by a heating step. Jenkner, U.S. Pat. No. 4,036,894, discloses bromination of bisphenol-A in acetic acid with recycle of the mother liquor and addition of alkaline or alkaline earth metal acetate.
Production of tetrabromobisphenol-A by dissolving bisphenol-A in methanol and adding liquid bromine is an effective way to make tetrabromobisphenol-A but the product contains various impurities which detract from its commercial value. These impurities include brominated phenols and hydrolyzable impurities. A need exists for a process that would lower the amount of these impurities.